April 18 (Reuters) - Russian gold and silver producer Polymetal International PLC says::First-quarter revenue rose 28 percent to $454 million from $354 million in the same period last year. .First-quarter gold equivalent output rose 27 percent to 374,000 ounces compared with 295,000 ounces last year. .Gold production in the first quarter was up 41 percent year-on-year, while silver output fell 15 percent due to a planned grade decline at the Dukat underground mine. .Gold output at the Kyzyl mine was at 78,000 oz with 92,000 oz produced in concentrate, it said. .Net debt rose 12 percent during the quarter to $1.704 billion as of March 31..Polymetal said it was on track to produce 1.55 million oz of gold equivalent in 2019. .